Transaction Management and Concurrency Control - ACID properties, serializability, lock-based concurrency control (2PL, deadlocks), time-stamping methods, optimistic methods - One Line Questions

1. What is a deadlock in the context of concurrency control? — A situation where two or more transactions are waiting indefinitely for each other to release locks
2. Starvation in concurrency control refers to: — A transaction being permanently prevented from executing or committing
3. What problem does the 'phantom read' phenomenon refer to? — A transaction re-executing a query and finding new rows that match the query criteria
4. What is a 'dirty read' phenomenon? — A transaction reads data that has been modified by another transaction but not yet committed
5. In Strict Two-Phase Locking (Strict 2PL), when are all locks released by a transaction? — At the commit or abort point of the transaction
6. What is the core idea behind optimistic concurrency control methods? — Assume conflicts are rare and check for them only at commit time
7. If a transaction fails after committing some of its operations, which ACID property guarantees that the changes are permanent? — Durability
8. Which ACID property ensures that concurrent transactions do not interfere with each other's execution? — Isolation
9. What does the 'A' in ACID properties stand for? — Atomicity
10. Which type of serializability guarantees that the result is equivalent to *some* serial order of execution? — Conflict Serializability
11. Which ACID property ensures that a transaction is treated as a single, indivisible unit of work? — Atomicity
12. The concept of 'serializability' is crucial for ensuring: — Data integrity in concurrent environments
13. In lock-based concurrency control, what type of lock is acquired when a transaction wants to read a data item? — Shared lock (S-lock)
14. During the validation phase of optimistic concurrency control, what is checked? — If the transaction's operations conflict with other concurrently committed transactions
15. What is a potential drawback of optimistic concurrency control? — It can cause frequent rollbacks if conflicts are high
16. What is the primary disadvantage of using Strict 2PL compared to basic 2PL? — It reduces concurrency by holding locks longer
17. If a transaction fails validation in an optimistic concurrency control system, what typically happens? — It is rolled back
18. Which of the following is a common strategy for handling deadlocks? — Transaction rollback
19. Which type of concurrency control method creates multiple versions of data items? — Multiversion Concurrency Control (MVCC)
20. Which timestamp-based concurrency control method assigns a unique timestamp to each transaction? — Time-stamping
21. A cycle in the wait-for graph indicates: — A deadlock
22. Which of the following is a common technique to prevent deadlocks by breaking cycles in the wait-for graph? — Preemption
23. What is the weakest isolation level, allowing transactions to read uncommitted data from other transactions? — Read Uncommitted
24. Which isolation level ensures that if a transaction reads a data item, subsequent reads of the same data item within that transaction will return the same value? — Repeatable Read
25. Which isolation level allows dirty reads? — Read Uncommitted
26. Which isolation level would prevent phantom reads? — Serializable
27. Which isolation level guarantees that a transaction will see only committed data? — Read Committed
28. Optimistic concurrency control methods typically involve three phases: — Read, Validate, Update
29. What is the strongest isolation level, guaranteeing that concurrent transactions produce the same result as some serial execution? — Serializable
30. Which of the following lock modes are compatible with each other? (S-lock with S-lock, S-lock with X-lock, X-lock with X-lock) — S-lock with S-lock
31. What type of lock is acquired when a transaction wants to modify a data item? — Exclusive lock (X-lock)
32. Which lock mode prevents any other transaction from reading or writing the data item? — Exclusive Lock (X-lock)
33. In MVCC, when a transaction reads a data item, which version does it typically access? — The version that was current when the transaction started
34. Which of the following is a key consideration when choosing a concurrency control method? — The expected frequency of conflicts
35. If a transaction T tries to read a data item X, and T's timestamp is less than WTS(X), what action is typically taken? — The read is rejected, and T is aborted
36. In time-stamping methods, what is the 'write timestamp' (WTS) of a data item? — The timestamp of the transaction that last wrote the data item
37. In time-stamping methods, what is the 'read timestamp' (RTS) of a data item? — The timestamp of the transaction that last read the data item
38. In write-ahead logging, before modifying a data item on disk, the change must first be written to: — The transaction log
39. If a transaction T tries to write a data item X, and T's timestamp is less than RTS(X), what action is typically taken? — The write is rejected, and T is aborted
40. In timestamp ordering, if a transaction T attempts to write a data item X, and T's timestamp is less than RTS(X), what is the outcome? — The write is rejected, and T is aborted.
41. What is the main advantage of time-stamping methods over basic 2PL? — They avoid deadlocks
42. Which method is used to detect if a transaction has been waiting for a lock for an excessively long time, potentially indicating a deadlock? — Lock timeout
43. What is the purpose of a 'commit record' in transaction logging? — To mark the successful completion of a transaction
44. What is the primary purpose of Two-Phase Locking (2PL)? — To ensure serializability
45. What is the primary goal of serializability in transaction management? — To ensure that concurrent execution of transactions produces the same result as some serial execution
46. What is a 'write-ahead logging' (WAL) technique primarily used for? — To ensure durability and atomicity of transactions
47. What is the 'wait-for graph' used for in deadlock detection? — To visualize dependencies between transactions waiting for resources
48. The Consistency property of ACID ensures that a transaction brings the database from one valid state to another. — True
49. Two transactions T1 and T2 are in conflict if they access the same data item and at least one of the accesses is a write operation. — True
All One Line Questions
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